Introduction: Peripheral nerve blocks after cesarean section (C-section) reduce post-operative use of analgesic agents. Transversus abdominis plane (TAP) block is an effective way to provide postoperative analgesia. TAP block with ropivacaine alone has not consistently been proven to be useful after C-section, and dexmedetomidine has not been studied as an adjuvant to ropivacaine for TAP blocks after C-section. Objective: To compare the combination of dexmedetomidine and ropivacaine to ropivacaine alone for TAP block after C-section for time to onset of pain and time to rescue analgesia. Materials and Methods: Forty American Society of Anesthesiology grade I or II patients undergoing C-section were enrolled in this randomized, controlled, double-blind study. Twenty patients each were allocated to two groups receiving bilateral TAP block. Test group received TAP block with 3 mg/kg of ropivacaine with 50 μg of dexmedetomidine. Control group received TAP block with 3 mg/kg of ropivacaine. Patient demographics, time to initial reporting of pain, time to first rescue analgesia, quality of block, and side effects were recorded. Results: Time to initial onset of pain (6.6 vs. 5.03 h; P = 0.01) and time to first rescue analgesia (7.8 vs. 6.47 h; P = 0.03) were significantly longer in the test group compared with control group. The two groups were similar in demographics and quality of block. No significant difference in side effects was noted between the two groups. Conclusion: Addition of dexmedetomidine to ropivacaine for TAP block in patients undergoing C-section prolonged the time to initial onset of pain and time to first rescue analgesia.

Cesarean section (C-section) is a very common surgery and recent estimates show that C-section rates in India range from 20% to 24% of all deliveries depending on the institution.[1],[2] Postoperative pain management is usually multimodal including oral or intravenous (IV) acetaminophen, nonsteroidal anti-inflammatory agents (NSAIDs) and opiates, epidural analgesia, and peripheral nerve blocks. Oral or IV analgesic agents have several limitations. Acetaminophen in lower doses (<2 g/day) is not an effective analgesic for moderate to severe pain, and high doses can cause acute liver failure. Similarly, using NSAIDs at high doses for moderate to severe pain can cause gastrointestinal injury. There is a potential risk of opiates being excreted in breast milk and these medications in high doses can lead to respiratory depression and death. Local analgesia can help reduce the use of oral or IV analgesic agent use while providing good postop pain control. Transversus abdominis plane (TAP) block with ropivacaine has been shown to reduce postop use of opiates after C-section.[3],[4],[5],[6] However, the results have not been consistent with some studies showing no additional postop pain control after TAP block with ropivacaine alone.[7],[8] Dexmedetomidine has been used as an adjuvant to ropivacaine in TAP block to increase the duration of analgesia after various abdominal surgeries.[9],[10],[11],[12] However, this combination has not been compared with ropivacaine alone for C-section.

Aims

The primary aim of this study was to compare the efficacy of the combination of dexmedetomidine and ropivacaine to ropivacaine alone in TAP block after C-section in terms of time to initial postoperative pain. Secondary aims included time to initial rescue analgesia and quality of TAP block.

Materials and Methods

This was a randomized, controlled, double-blind study that was conducted over a 14-month period. The Hospital Ethics Committee approved the study. This article adheres to the applicable CONSORT guidelines.

Inclusion criteria

All patients (a) above 18 years of age, (b) undergoing C-section under spinal anesthesia, (c) American Society of Anesthesiology (ASA) grade 1 or 2, (d) who could understand and rate their pain on Visual Analog Scale (VAS; scale of 0–10), and (e) provide written informed consent were eligible for enrollment in the study.

Exclusion criteria

Patients who (a) were unwilling to participate in the study, (b) had a history of anaphylaxis with ropivacaine or dexmedetomidine use, (c) had a history of drug abuse, (d) were unable to understand VAS, (e) had coagulopathy, (f) who did not tolerate spinal anesthesia well and had to be converted to general anesthesia for C-section, (f) had C-section planned with general anesthesia, or (g) could not provide informed consent were excluded from the study.

Group allocation, randomization, and blinding

After obtaining informed consent, the patients were assigned to one of the two groups, that is, test and control. Test group received bilateral TAP block with 3 mg/kg of ropivacaine (rounded to nearest multiple of 10) plus 50 μg of dexmedetomidine diluted to total of 40 mL in normal saline with 20 mL on each side. Control group received bilateral TAP block with 3 mg/kg of ropivacaine (rounded to nearest multiple of 10) diluted to total of 40 mL in normal saline with 20 mL on each side.

Bilateral TAP block was performed on all the study patients according to their coded group allocation immediately at the end of surgery in the operating room. The US probe was placed transverse to the abdomen (horizontal plane) in the mid-axillary line between the costal margin and the iliac crest on one side. The layers of external oblique, internal oblique, and transversus abdominis were identified on ultrasound in each patient. A 100-mm short bevel needle was introduced in plane of the ultrasound probe and advanced until it reached the plane between the internal oblique and transversus abdominis muscle. Upon reaching the plane, a small volume of local anesthetic (1 mL) was injected to confirm the correct needle position after which the remaining dose (19 mL) of local anesthetic was given. The same process was repeated on the other side.

Postoperative monitoring

After completion of TAP block, each patient was moved to the postoperative recovery room for monitoring of vitals, pulse oximetry, postoperative pain, and adverse effects. Each patient was asked to rate the postoperative pain using VAS scale. Time to initial reporting of postoperative pain was then noted. The time period when the patient's VAS score was 4 was also noted and rescue analgesia was provided with IV tramadol 1 mg/kg (rounded to nearest multiple of 10). The quality of anesthesia was assessed by the anesthesiologist as excellent/good/fair. Each patient completed the study at the time of receiving rescue analgesia. Patients who did not report any postoperative pain completed the study after observation for initial 24 h of postoperative period.

Data collection

Each patient's age, weight and height, time to initial post-operative pain, VAS at initial reporting of pain, time to rescue analgesia, quality of block as assessed by the anesthesiologist, and adverse events were reported.

Sample size calculation

Based on the previous literature, it was estimated that addition of dexmedetomidine to ropivacaine would result in delay in reporting of significant postoperative pain by 1.1 h with a standard deviation of 1.22 h.[11] To detect this difference with a power 80% and alpha 0.05, a sample of size of at least 39 patients was required. This number was rounded to 40, 20 in each group.

In all, 40 patients (20 in each group) were enrolled during the study period and completed the study. Two patients, one in each group, did not report pain until 24 h after the surgery. The two groups were comparable in terms of age, weight, height, ASA grade, VAS at initial reporting of postoperative pain, and quality of block as assessed by the anesthesiologist [Table 1]. The mean time to initial reporting of postoperative pain was significantly higher in the test group (6.6 ± 2.01 h) when compared with control group (5.03 ± 1.34 h; P < 0.01). The mean time to first rescue analgesia was significantly higher in the test group (7.8 ± 2.29 h) when compared with control group (6.47 ± 1.22 h; P < 0.05).

Table 1: Comparison of demographics and clinical features between the test and control groups

This is the first study to analyze the effect of dexmedetomidine combined with ropivacaine in US-guided TAP block for postoperative pain relief among parturients undergoing C-sections. The study shows that addition of dexmedetomidine to ropivacaine resulted in a longer mean time to initial reporting of significant postoperative pain (6.6 vs. 5.03 h; P = 0.01) and time to initial rescue analgesia (7.8 vs. 6.47 h; P = 0.03) when compared with ropivacaine alone.

The combination of ropivacaine and dexmedetomidine (RD) has been compared with ropivacaine alone for US-guided TAP block in only four studies before albeit with different results. One study showed that US-guided TAP block with RD reduced overall patient-controlled analgesia (PCA) use in patients undergoing abdominal hysterectomy when compared with ropivacaine alone.[9] Another study showed that in patients undergoing lower abdominal surgeries, TAP block with RD reduced postoperative pain score on VAS scale up to 12 h when compared with ropivacaine alone.[10] Similarly, a study by Xu et al. showed that TAP block after emergency abdominal surgery with RD reduced the postoperative pain score on VAS scale up to 12 h, increased the time to first use of PCA (248.5 vs. 157.5 min), and reduced the overall use of PCA when compared with ropivacaine alone.[11] However, the study conducted by Ding et al. in patients undergoing gastrectomy did not show any difference in postoperative pain score or opiate use between RD and ropivacaine alone.[12] The results of this and previous studies suggest that addition of dexmedetomidine to ropivacaine in TAP block may improve postoperative pain and/or postoperative PCA use in patients undergoing lower abdominal surgeries.

Bupivacaine has been used as another local anesthetic agent with dexmedetomidine in TAP block in two studies. One study showed that TAP block after abdominal hysterectomy with bupivacaine and dexmedetomidine (BD) increased the mean time to first use of morphine (470 vs. 280 min), decreased the total dose of morphine used postop, and had a lower VAS score at 8 h after surgery when compared with bupivacaine alone.[13] Another study showed that TAP block with BD improved VAS score up to 24 h after surgery and reduced overall postop morphine use when compared with bupivacaine alone.[14] Based on these studies, it seems that either ropivacaine or bupivacaine in combination with dexmedetomidine may have comparable analgesic effect after lower abdominal surgeries. However, formal head-to-head comparison between RD and BD for TAP block is needed to test this hypothesis.

Several studies have explored other adjuvants with ropivacaine for TAP blocks. Addition of fentanyl to ropivacaine for TAP block after C-section in one study did not have any effect on mean time to first use of PCA, overall use of PCA, or postoperative VAS scores when compared with ropivacaine alone.[15] Combination of dexamethasone to ropivacaine (Dex-R) for TAP blocks has also yielded inconsistent results in different studies. In one study, TAP block after inguinal hernia repair with Dex-R was associated with lower pain score at 24 h postop and lower morphine use in the first 24 h after surgery.[16] Similarly, TAP block with Dex-R combination was associated with lower VAS score 12 h after surgery, longer time to first tramadol use, and total tramadol use when compared with ropivacaine alone after abdominal hysterectomy.[17] However, another study showed that TAP block with Dex-R and ropivacaine did not differ in terms of postop pain score after inguinal hernia repair and spermatocelectomy.[18] Therefore, dexamethasone may not be as effective an adjuvant as dexmedetomidine to combine with ropivacaine for TAP blocks. However, these two combinations will need to be compared with each other for a definitive conclusion.

The study has some limitations. The study was not designed to assess the effect of addition of dexmedetomidine to ropivacaine in reducing postoperative opiate use after C-section. The follow-up period for postoperative pain was short in this study. A larger sample size would be required to assess these end-points, which was not feasible within the time frame planned for this study. The results of the study are applicable to ASA class I and II pregnant women in India.

In conclusion, this study shows that addition of dexmedetomidine to ropivacaine for TAP block after C-section leads to delay in time to onset of pain and use of rescue analgesia.